Switchgear assemblies are typically used to connect a plurality of electrical loads to a common electrical bus. Such assemblies are typically provided with a plurality of switching devices having one side connected to the common bus and the other side connected to various electrical loads; these switching devices provide electrical protection to isolate the loads during abnormal current conditions, such as an overload or a short circuit condition.
Switchgear often comprises an earthing switch which allows either the line or bus terminals to be grounded for personnel safety. That is particularly important during maintenance operations, but also during normal function of the switchgear assemblies. Prior to earthing the line or bus terminals, it is mandatory to disconnect the upstream source of electrical power supplying the switchgear assembly; however, under certain conditions, it may happen by mistake to ground a live circuit. Another dangerous situation arises when the upstream source of electrical power is inadvertently reenergized during bus maintenance before performing closing of the switch. In both such situations, it is necessary to prevent wounds to personnel and damage to equipment by a correct functionality of the earthing switch used.
At the present, many kinds of earthing switches are known and used. For example, the patent U.S. Pat. No. 4,490,595 discloses an earthing switch which comprises a moving blade contact movable about a fulcrum and a fixed blade contact having an aperture at one end to define side walls which form spaced fixed contacts. In the open position of the switch, said moving blade is parallel to the fixed blade contact; during closing of the switch, the moving blade contact enters in said aperture from the closed end thereof and moves to the region of the current contacts until it comes into contact with an insulating stop disposed underneath the fixed blade contact. Thus, in the closed position of the earthing switch the moving blade is perpendicular to said blade fixed contact.
European patent application EP A 0592338 discloses an earthing switch which is actuated by means of an interlocking device controlled by an operating unit associated with another switch; said interlocking device moves suitable mechanisms which actuate a shaft with a plurality of mobile contacts, these latter being suitable for contacting corresponding fixed contacts by a rotary movement around a fixed axis.
At the present state of the art, known earthing switches even though performing properly the functions required, still have drawbacks and present some aspects which deserve improvements. In fact, in many cases they have a structure that is not suitable for assuring an optimised functionality of the earthing switch; in particular it does not assure an optimised contact pressure which allows contrasting the magnetic repulsion forces generated especially during the closure operation on a live circuit.
Also, the traditional layout of the components and traditional movement systems of the mobile contacts are carried out by a high number of elements which are assembled each other according to cumbersome and complicated solutions. Moreover, some earthing switches have a configuration which do not allow their easy insertion in the structure of a switchgear. Such condition increases costs and time for installation, and affects also the reliability.
Hence, it is evident the need to have technical solutions that represent a valid alternative to the known earthing switches.